The present invention generally relates to RAKE receivers and particularly relates to the computation of the RAKE “combining weights” used in such receivers.
RAKE receivers represent a well-known approach to multipath reception, particularly in Direct Sequence Code Division Multiple Access (DS-CDMA) wireless communication systems. With multipath, a transmitted signal follows multiple propagation paths and the intended receiver thus receives multiple “versions” (images) of the transmitted signal, with each signal image generally suffering from different path delay, phase, and attenuation effects.
RAKE receivers exploit multipath by allocating each of two or more RAKE “fingers” to one of the incoming signal images. In that sense, then, each finger is tuned to a particular one of the multipath components of the incoming composite received signal and each finger thus receives its own version of the originally transmitted signal. By estimating the channel effects, e.g., phase and attenuation, and by properly accounting for the differences in path delays, the individual output from each finger may be RAKE combined with the outputs from the other fingers to provide a combined RAKE output signal whose signal-to-noise ratio (SNR) generally is improved by the summed contribution of each finger's despread output signal.